（1）
A - C = pi/3
A + C = pi - B
所以 ：
2A = 4pi/3 - B
即：A = 2pi/3 - B
C = pi - A - B
= pi/3 - B/2
（2）
由正弦定理及“a+c=2b”,得：
sinA + sinC = 2sinB
sinA + sinC = 2sin((A+C)/2)cos((A-C)/2)
= 2cos(pi/2 - (A+C)/2) cos(pi/6)
= 2cos(B/2) * √3/2
= √3cos(B/2)
2sinB = 4sin(B/2)cos(B/2)
所以：
√3cos(B/2) = 4sin(B/2)cos(B/2)
所以：
cos(B/2) = 0（B=pi,故舍去）
或sin(B/2) = √3/4
因此：
cos(B/2) = √13/4
sinB = 2sin(B/2)cos(B/2) = √39/8